Recovery of cyclodienes with vapor phase cracking



y 1957 J. F. NELSON ET AL 2,801,270

RECOVERY OF CYLODIENES WITH VAPOR PHASE CRACKING Filed Nov. 16. 1953 a:to

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"@251 M fv vLi P H JOSE H FJIELSQ mason w. HUBBARD 0r ATM/HIE) UnitedStates Patent C) RECOVERY OF CYCLODIENES WITH VAPOR PHASE CRACKKNGJoseph F. Nelson and Fred W. Banes, Westfield, and Addison W. Hubbard,Cranford, N. J., assignors to Esso Research and Engineering Company, acorporation of Delaware Application November 16,1953, Serial No. 392,322

4 Claims. (Cl. 260-666) This invention relates to a process forrecovering high purity cyclopentadiene and methyl cyclopentadiene fromcrude concentrates of their dimers, codimers, trimers, and cotrimers,subjected to a vapor phase cracking. The vapor phase cracking is mademore eflicient by including a continuous undercutting step for removingcertain high-boiling ends between a tubular preheater of the feed andthe cracking tube. Preheating of the crude dimers, codimers and higherpolymers in a continuous stream partly maintained in liquid phasefollowed by continuous removal of the heavier liquid ends of the preheatfeed brings about a significant reduction in coking of the crackingtube.

Vapor phase cracking of the cyclodiene dimers and higher polymers cangive higher conversions to the monomers as compared to liquid phasecracking, but a serious problem associated with vapor phase cracking isthe coking of the cracking tube. It is known that in the past someproposed processes have dealt with vapor phase cracking of a very narrowboiling range cyclopentadiene dimer fraction substantially free of othercyclopentadiene polymers. It has been indicated that for such vaporphase cracking large amounts of gaseous diluents or other measuresshould be employed to prevent undesired forrnation of coke and/or highpolymer resins. Such measures described in the past have not been foundsuitable for a process of recovering both cyclopentadiene monomer andmethylcyclopentadiene monomer from a crude mixed dimer and polymerstream. For one thing, the use of a large amount of gaseous diluent canbe upsetting to the recovery of the separate monomers. Also diflicultiesarise in making a suitable separation of heavy ends between a feedpreheater and a cracking tube if gaseous diluents are used improperly.

The technique of the present invention is designed to minimize coking ofthe cracking tube while obtaining improved recovery of both high puritycyclopentadiene and methyl cyclopentadiene. It has been demonstrated tobe efiicient without the use of any gaseous diluent.

The invention will be described by reference to the flow diagram in thedrawing. Here the crude feed of cyclodiene dimer and polymers issupplied by line 1 to the preheater 2 surrounded by suitable heatingmedium as in furnace 3. A high boiling recycle fraction is admixedthrough line 4 with the feed entering the preheating tube 2.

The preheating tube 2 operates with an outlet temperature of about 250to 300 F. and with pressures of about 1 to 30 p. s. i. a. maintainedtherein. Using a liquid feed rate of 15 to 50 volumes per unit vaporizervolume per hour the feed may be almost completely "ice vaporized onleaving the outlet of the preheating tube 2. Since there is always someliquid flow in this preheating or vaporizing tube and since temperaturesare below 300 C., no coking occurs while an appreciable 5 amount ofcracking of dimer takes place therein.

The preheated liquid and vapor mixture is discharged from the outlet ofthe preheater tube 2 to line 5 into the flash drum 6. The drum 6 acts asa bottoms knockout to continuously remove heavy ends boiling mainlyabove about 275 C. to 280 C. while vaporized and partially crackedproducts are separated, e. g., withdrawn overhead by line 7. The bottomsare continuously withdrawn through line 8 from drum 6. Bailles, 9,provided in the upper part of drum 6 help to knock out entrained heavyends which are to be prevented from entering the cracking tube or coils,10, with the vapors sent therethrough through line 7.

The cracking tube 10 is heated by surrounding heating gases or heatingmeans as in furnace 11.

In the cracking tube 10, the cracking of the dimers, codimers, trimersand cotrimers of the C5Ce cyclodienes is completed at temperatures of350 to 450 C. in contact times of 0.5 to 3.5 seconds. To obtain shortcontact time a vapor velocity in the range of 200 to 300 feet per secondis used. With the refractory type high boiling polymers absent, cokingdifliculties are substantially reduced in the cracking tube.

If any gaseous diluent is to be added, e. g., steam or inert hydrocarbongas, it would be introduced into the flash drum 6 through inlet 12. Theintroduction of the diluent means a decrease in capacity with a unitdesigned to operate without the use of a diluent.

The cracking tube effluent in passed from an outlet of the cracking tube10 through a heat exchange cooler 13 by line 14 into an intermediatepart of a splitter tower 15. The splitter tower 15 is a fractionatingmeans for removing cyclopentadiene and methyl cyclopentadiene monomerscontinuously as an overhead vapor stream and continuously removingdimers and higher polymers as a bottoms. The overhead vapor stream istaken off from tower 15 through line 16. The bottoms are withdrawn fromtower 15 through line 17. A portion of the bottoms may be recycledthrough line 18 and reboiler 19 to a bottom part of the tower 15.Another portion of the bottoms may be purged from the system throughline 20. Any desired portion of the bottoms may be passed through line21 into the recycle line 22 for return to the preheater feed line 1.

The splitter tower 15, equipped with about 10 to 15 plates forfractionation is operated at an overhead temperature of about 50-60 C.using reflux ratio of from 1:1 to 5:1. The overhead monomer vapors maybe cooled in condenser 23 in being passed to the receiver 24. Reflux isreturned to the upper part of tower 15 through line 25. Distillate ofthe monomer is passed from receiver 24 through line 26 into the nextfractionating column 27.

If steam distillate has been used in the cracking tube water condensatewould have to be withdrawn through line 28. Any gaseous diluent would beremoved from receiver 24 by vent line 29. A suitable bottoms temperaturein the splitter tower 15 is of the order of to C. An intermediatefraction of C7-C9 hydrocarbons, such as would include C7 cyclodienes, isadvantageously purged as a side stream 30 below the feed splitter tower15 supplied to the next tower 27 should be principally C5 and Cscyclodienes. Some dimerization and further polymerization takes place inthe splitter tower 15 to yield the bottoms which may be recycled to thepreheater coil 2.

Column 27 which is used for separating the C5 and Ca cyclodiene monomersmay be fed at a midpoint with the mixture of the monomers and may beprovided with about 30 plates. In column 27 the overhead product istaken oif at a vapor temperature of about 40 to 43 C. at a reflux ratioof 2:1 to 5:1. Generallyit is preferable for this overhead product to bea high purity cyclopentadiene monomer.

The methyl cyclopentadiene product is advantageously taken 011 as a sidestream from a lower part of the column 27, below the feed inlet, e. g.,at about the 5th plate from the bottom and at a temperature of about 73-80 C. In column 27, additional dimerization and polymerization occursto yield a bottoms product.

The bottoms is withdrawn from column 27 through line 36. A portion ofthe bottoms may be recycled through reboiler 37 and line 38. Any portionof the bottoms from column 27 which will not be recracked may be purgedthrough purge line 39. The portion of the bottoms from column 27 to berecracked may be recycled by way of line 22 and line 4 to the inlet ofthe preheater coil 2. A mixed purged stream may be removed from thesystem through line 41. Some purging is desirable to prevent the buildupof high boiling polymers and other fill in the recycle streams.Ordinarily, it is desirable to hold the recycle rate in the range offrom /2 to 5 halves of the fresh feed.

The general kind of crude feed for which the present process is adaptedis one which will contain about 35 to 45% cyclopentadiene (CPD) in theform of dimer and codimers, 30 to 35% methyl cyclopentadiene (MCPD) inthe form of dimer and codimers and contain in the remaining 35 to 20%,C7 cyclodienes and acylic dienes as dimers and codimers, and somearomatics and higher polymers. It will have an initial boiling point ofabout 135 C. and contain 9 4-98 volume percent boiling up to about 280C. and from 2 to 6 volume percent boiling higher than about 280 C. Amore detailed analysis of a representative fresh feed is shown in thefollowing Table I.

TABLE I Analysis of fresh feed [Vacuum Dlst.]

Boiling Wt. Wt. Percent of Total in Fraction Out No. Range, Percent C.at 1 on Atmos. Feed CPD MCPD 134-157 12. 51 4. 5 3. 9 157-170 4. 27 5.3 1. 170-171 11. 12 20. 9 3. 5 CPD Dimer. 171-175 11. 22 21. 7 5. 7175-184 10. 56 15.1 11.5 CPD-MCPD 184-187 11. 24 12. 16. 7 Oodimer.187-193 10. 50 10. 17. 2 193-199 10.33 4.3 20. 9 MCPD Dimer 199-209 9.49 3. 4 13. 2 209-280 3. 26 2. 1 5.0

Residue 5. 50 0. 2 0. 7

The total feed in this case contained 36.1 wt. percent CPD and.36.8 wt.percent MCPD. These data, as well as those from which the figures inTable I were derived, were obtained by cracking the feed or fractionsthereof at 400 F. The monomer products thus formed were then subjectedto mass spectrometer analyses.

Another sample of feed was cracked at 400 Fraud analyzed for total CPDand MCPD in the manner described above. A sample of this same feedwas'then analyzed directly in the mass spectrometer to determine thequantities of dimers and codimers. These data are given in Table II.

4 TABLE II Analysis of fresh feed Mass Wt. percent on No. Total FeedCyclopentadiene (as monomer) 66 37. 5 CPD Combined in Feed as OPD D1mer132 21.0 OPD Combined in Feed as CPD-MCPD Codimers 146 14. 4lllethylcyclopentadicne (as Monomer) 80 33.9 MCPD Combined in Feed asMCPD Dimer 160 12. 7 MCPD Combined in Feed as MCPD-CPD Codimer 146 17. 4

Wt. percent of CPD as:

CPD Dlmer CPD-MCPD Ood Wt. percent of MCPD as:

MCPD Dimer MCPD-CPD Codimers ing feed boiling as high as 195 C. orhigher. If methylcyclopentadiene is also to be recovered the feedendpoint is 210 C. or preferably 275 280 C.

EXAMPLE 1 When using the feed described in Table I and operating thepreheating or vaporizing tube with an outlet temperature of 225 C. thenundercutting the preheater effluent in a knockout or flash drum, a purgestream of heavy material representing 2 volume percent of the feed wascontinuously removed as bottoms. When this heavy purge material wassubjectedto cracking at 425 C. there was recovered only 12% ofcyclopentadiene and methyl cyclopentadiene monomers based on the amountof purge stream and' at the same time there was considerable cokeformation in the cracking tube. In comparison thereto the material whichis vaporized at up to 280 C. and thus removed from the knockout drum iseasily cracked completely at 400 C. leaving no coke residue.

EXAMPLE 2 A fraction of the feed described in Table II, containing 37.5wt. percent CPD and 33.9 wt. percent MCPD as dimers and codimers, wascut to have a boiling range of about 270 to 276 C. so as to containcyclopentadiene trimer. This material was easily cracked at 400C. at 1.5seconds contact time with relatively little coke formation. Therecovered cyclopentadiene monomers represented 97% of the theoreticalyield. In contrast, cracking materials including tetramers of thecyclodienes boiling above 280 C. gave very low yields of the C5-C5cyclodiene monomers and caused excessive coke formation. This indicatesthe refractory nature of the components boiling above the range of theC5 to Ca cyclodiene trimers, i. e., boiling above 280 C.

' EXAMPLE 3 A concentrate of cyclodiene dimers, codimers and higherboiling components, yielding 42.2% cyclopentadiene, 34.4% methylcyclopentadiene with 5% of C7 cyclopentadienes, C5 acyclic dienes, and14% of other hydrocarbons including aromatic, olefins and high boilingpolymers, was used in a series of vapor phase cracking experiments. Theoverall feed boiled in the range of 135 to above 280 C., volume percentdistilling oif at about 280 C. The feed was cracked at 400 C. in 1.5seconds contact time at a vapor velocity of 2.5 per second. The totalrun length was 15-20 hours.

After each run the cracking tube was washed thoroughly with a lighthydrocarbon to remove any soluble residue and the remaining insolubleresidue deposited on the tubes was burned out at 1100 F. by passing airthrough the tube. The combustion gases were caught in a conventionalDrierite-Ascarite type train to determine the amount of Water the carbondioxide evolved. These gas evolutions were used to estimate thequantities of coke deposit in the cracking tube. Data illustrating theadvantages of continuously undercutting the cracking feed to preventmaterial boiling above 280 C. from entering the cracking tube is shownin the following table:

Table III Relation of coke deposits to feeds Wt. Per- Wt. Percent uncentCoke deroutting Deposition on Total based on It is evident from datasuch as shown in Table II that continuous removal of high boilingrefractory bottoms from fresh and recycle feed is necessary. It is alsonecessary to remove a certain amount of the fresh feed or mixed feeds byundercutting to prevent high boiling materials boiling about 280 C. fromentering the cracking tube. Thus it can be seen that it is desirable tohave any recycle which is to be admixed with the fresh feed pass throughthe preheater or vaporizer to be subjected to the similar undercutting.

Examination of the cracking tube before burn out showed that coke tendedto be deposited at the entrance of the high temperature cracking tubewhen heavy ends boiling above 280 C. were permitted to enter thecracking tube and these deposited residues were the chief source ofcoke.

Having described the invention it is claimed as follows:

1. A process of recovering Cs and Cs cyclodiene monomers which comprisespreheating in a continuous stream a crude condensate containingcyclodiene dimers, codimers, trimers and cotrimers, boiling in the rangeof about 135 to 280 C. and a minor amount of higher boiling componentsboiling above about 280 C., said higher boiling components containingcyclodiene tetramers which when subjected to vapor phase cracking formcoke, preheating said condensate to vaporize the dimer, codimer andtrimer components, boiling up to about 280 C., maintaining said higherboiling components including the cyclodiene tetramers in liquid phase,separating the vaporized arated from the remaining vapors of saidstream, and subjecting said remaining vapors in continuous stream ofrestricted cross section to the vapor phase cracking.

3. In the recovery of C5 and Cs cyclodienes as monomers from a crudemixture of their dimers, codimers, trimers, cotrimers and higherpolymers, preheating said mixture to vaporize components boiling up to280 C., separating components thereof boiling above 280 C. includingsaid higher polymers as liquids, vapor phase cracking the separatedvapor components kept free of said components boiling above 280 C. in acontinuous stream, cooling the vapor phase cracked vapor components andintroducing them into a first fractionation zone, separating an overheaddistillate of cyclopentadiene and methyl cyclopentadiene from said firstfractionation zone, removing a side stream of C7 to C9 components in alower part of said first fractionation zone below its feed point, andwithdrawing a liquid dimer containing fraction from a bottom part offirst fractionation zone, passing the overhead distillate from saidfirst fractionation zone into an intermediate part of a secondfractionation zone, distilling overhead from said fractionation zonecyclopentadiene monomer, withdrawing a side stream of methylcyclopentadiene monomer between the bottom and the feed inlet of saidsecond fractionation zone and withdrawing dimer containing liquidbottoms from a bottom part of said second fractionation zone, andrecycling dimer-containing bottoms fractions from said fractionationzone to the preheating zone.

4. In the process of claim 3, supplying an inert lower boiling diluentto the vapors passed through said vapor phase cracking zone, andseparating said diluent from the overhead distillate of the firstfractionation zone before the hydrocarbon distillate containingcyclopentadiene and methyl cyclopentadiene is supplied to said secondfractionation zone.

References Cited in the file of this patent UNITED STATES PATENTS2,240,160 Kaplan Apr. 29, 1941 2,535,418 Holland Dec. 26, 1950 2,582,920Businger et al Jan. 15, 1952

1. A PROCESS OF RECOVERING C5 AND C6 CYCLODIENE MONOMERS WHICH COMPRISESPREHEATING IN A CONTINUOUS STREAM A CRUDE CONDENSATE CONTAININGCYCLODIENE DIMERS, CODIMERS, TRIMERS AND COTRIMERS, BOILING IN THE RANGEOF ABOUT 135* TO 280*C. AND A MINOR AMOUNT OF HIGHER BOILING COMPONENTSBOILING ABOVE ABOUT 280*C., SAID HIGHER BOILING COMPONENTS CONTAININGCYCLODIENE TETRAMERS WHICH WHEN SUBJECTED TO VAPOR PHASE CRACKING FORMCOKE, PREHEATING SAID CONDENSATE TO VAPORIZE THE DIMER CODIMER ANDTRIMER COMPONENTS, BOILING UP TO ABOUT 280*C., MAINTAINING SAID HIGHERBOILING COMPONENTS INCLUDING THE CYCLODIENE TETRAMERS IN LIQUID PHASE,SEPARATING THE VAPORIZED COMPONENTS WHICH BOIL IN THE RANGE OF 135* TO280*C. FROM THE LIQUID PHASE AND SUBJECTING TO VAPOR PHASE CRACKING SAIDVAPORIZED COMPONENTS FREE OF COMPONENTS HIGHER BOILING THAN 280*C.INCLUDING CYCLODIENE TETRAMERS AT TEMPERATURES IN THE RANGE OF ABOUT350* TO 450*C.